Thin planar semiconductor device having electrodes on both surfaces and method of fabricating same

ABSTRACT

A thin, planar semiconductor device having electrodes on both surfaces is disclosed. This semiconductor device is provided with an IC chip and a wiring layer having one side that is electrically connected to surface electrodes of the IC chip. On this surface of the wiring layer, conductive posts are provided on wiring of the wiring layer, and an insulating resin covers all portions not occupied by the IC chip and conductive posts. The end surfaces of the conductive posts are exposed from the insulating resin and are used as first planar electrodes. In addition, a resist layer is formed on the opposite surface of the wiring layer. Exposed portions are formed in the resist layer to expose desired wiring portions of the wiring layer. These exposed portions are used as second planar electrodes. Stacking semiconductor devices of this construction enables an improvement in the integration of semiconductor integrated circuits.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and to a methodof fabricating the semiconductor device, and in particular, to theconstruction of a semiconductor device that can be three-dimensionallystacked and to a method of fabricating the semiconductor device.

2. Description of the Related Art

With the rapid development of Internet technology, prior-artconstructions such as mainframes and terminals that are connected tomainframes have been replaced by systems made up by servers that aredistributed throughout the world and the high-speed communication linesthat connect them.

This information communication network is now rapidly coming intopopular use in households and by individuals through inexpensive andhighly functional personal computers or mobile telephones that can beconnected to the Internet, and as a result, the next-generation Internetprotocol (IPv6) will allow connection of all types of electricalhousehold appliances to the Internet. It is desirable that the LSI thatis incorporated in these mobile telephones and information electricalappliances be capable, by itself, of various types of processing rangingfrom information processing and information saving to input/outputcontrol. SoC (System on Chip), in which various function blocks areformed on a single LSI chip to realize a high-level multifunctionalinformation processing system, is now receiving increased attention. Inactuality, however, the simultaneous formation of various functionblocks requiring different forming processes on a silicon wafer isproblematic both in terms of design as well as fabrication. There is theadditional problem that such LSI lacks flexibility when specificationsare to be modified, such as when modifying the design or extending thefunctionality of each block.

In recent years, SiP (System in Package), in which a plurality ofseparate LSI are integrated into a package and systemized, has showngreat promise as a countermeasure to this problem. In particular, in apackage in which each individual LSI is provided as a separate moduleand then stacked three-dimensionally, each module is first tested toensure against defects before being integrated. As a result, a higheryield of products that are free of defects and a higher degree ofintegration through three-dimensional packaging can be obtained than foran SoC in which a large number of functional elements are formedsimultaneously or an SiP in which non-modular chips are stacked.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novelsemiconductor device and a method of fabricating the semiconductordevice that can provide a solution to the above-described problems ofthe prior art, and in particular, that enables an improvement inintegration through three-dimensional packaging.

In the semiconductor device of the first aspect of the presentinvention, surface electrodes of an IC chip are electrically connectedto one surface of a planar wiring layer that is constituted byelectrical wiring. Further, conductive posts are provided on the wiringof the wiring layer on one surface of the wiring layer, and aninsulating resin covers areas in which the IC chip and conductive postsare not provided. The end surfaces of the conductive posts are exposedfrom the insulating resin.

A resist layer is formed on the opposite surface of the wiring layer.Exposed portions in which desired wiring portions of the wiring layerare exposed are formed in this resist layer.

According to the first aspect of the present invention, the end surfacesof the conductive posts on one surface of the wiring layer can be usedas first planar electrodes, and the exposed portions of the wiring onthe other surface of the wiring layer can be used as second planarelectrodes.

In the first aspect of the semiconductor device, first electrodeterminals may be formed on the end surfaces of the conductive posts.Second electrode terminals may also be formed on the wiring in theexposed portions. Ball-shaped solder may be used for the first electrodeterminals and for the second electrode terminals.

The method of fabricating the semiconductor device of theabove-described first aspect involves the following steps of:

preparing a wiring substrate that is constituted by a base material anda wiring layer that is composed of wiring that is formed on this basematerial, and an IC chip having electrode terminals formed on itssurface;

providing conductive posts on desired wiring of the wiring layer of thewiring substrate;

connecting the surface electrodes of the IC chip to desired wiring ofthe wiring layer of the wiring substrate;

covering the IC chip and the conductive posts that have been arranged onthe surface of the wiring layer of the wiring substrate and conductivebumps with an insulating resin;

removing the base material from the wiring substrate to expose thewiring layer;

forming a resist layer on the exposed wiring layer with the exception ofdesired wiring portions; and

grinding away the insulating resin to expose the end surfaces of theconductive posts.

The present invention thus can provide a stackable semiconductor devicethat lacks package material, thereby enabling a thin construction and agreater degree of freedom in design. The present invention thereforeenables the realization of a high-capacity memory module or aSystem-in-Package.

As a second aspect, the present invention provides an assembled unit inwhich a plurality of semiconductor devices of the above-described firstaspect is stacked. This assembled unit can be produced by electricallyconnecting the exposed portions of the wiring layer of one semiconductordevice to the end surfaces of the conductive posts of anothersemiconductor device among the stacked semiconductor devices.

Finally, as a third aspect, the present invention provides asemiconductor device in which a planar wiring layer that is composed ofwiring that is electrically connected to the end surfaces of conductiveposts is provided in the semiconductor device of the first aspect. Inthis aspect, first electrode terminals may be formed on the wiring ofthe planar wiring layer that is made up by wiring that is electricallyconnected to the end surfaces of the conductive posts, and secondelectrode terminals may be formed on wiring of the exposed portions.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description withreference to the accompanying drawings, which illustrate examples of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the semiconductor device according to thefirst embodiment of the present invention.

FIGS. 2A–2E show the fabrication steps of a semiconductor deviceaccording to the first embodiment example of the present invention.

FIG. 3 shows the semiconductor device according to the second embodimentof the present invention.

FIG. 4 shows the semiconductor device according to the third embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With the first working example of the semiconductor device of thepresent invention, referring to FIG. 1, IC chip 1 is arranged on onesurface 3 a of planar wiring layer 3. Wiring layer 3 is a layer composedof wiring such as signal lines, power supply lines, and ground lines.Electrodes 2 on the surface of IC chip 1 are electrically connected todesired wiring of wiring layer 3.

Wiring layer 3 is a structure in which a wiring substrate is formed byforming wiring on the surface of a planar base material, following whichthe base material is removed. IC chip 1 is a structure that has beenmade thin by grinding the rear surface.

On one surface 3 a of wiring layer 3, protruding conductive posts 6 areelectrically connected to the wiring that constitutes wiring layer 3.Although conductive posts 6 are formed as separate structures from thewiring of wiring layer 3 in this case, they may also be formed as asingle unit with wiring layer 3. The height of conductive posts 6 isequal to the height of the rear surface of IC chip 1 that is arranged onthe same surface 3 a of wiring layer 3.

Still further, the vicinity of IC chip 1 and conductive posts 6 on thissurface 3 a of wiring layer 3 is covered with insulating resin 7. Atleast end surfaces 8 of conductive posts 6 are exposed from resin 7.

Solder resist layer 9 is formed on the opposite surface 3 b of wiringlayer 3. Exposed portions 10 for exposing desired wiring of the wiringthat constitutes wiring layer 3 are formed in this solder resist layer9. In other words, desired wiring portions on the opposite surface 3 bof wiring layer 3 are not covered by solder resist layer 9.

According to the above-described construction, end surfaces 8 ofconductive posts 6 on one surface 3 a of wiring layer 3 can be used asfirst planar electrodes, and exposed portions 10 of wiring on theopposite surface 3 b of wiring layer 3 can be used as the second planarelectrodes.

In addition, ball-shaped solder may be affixed as electrode terminals toboth or either of end surfaces 8 of conductive posts 6 and exposedportions 10 of the wiring of wiring layer 3 that are not covered bysolder resist layer 9.

Explanation next regards the method of fabricating the above-describedsemiconductor device.

First, as shown in FIG. 2A, wiring substrate 4 is prepared that isconstituted by base material 5 and wiring layer 3 in which electricalwiring is formed such as signal lines, power supply lines, and groundlines. Conductive posts 6 are then provided on the wiring thatconstitutes wiring layer 3. IC chip 1 in which bumps are used on surfaceelectrodes 2 is also prepared.

Next, as shown in FIG. 2B, surface electrodes 2 of IC chip 1 areelectrically connected (flip-chip attachment (FCA)) to the wiring ofwiring layer 3 on wiring substrate 4.

Insulating resin 7 as shown in FIG. 2C next covers IC chip 1 andconductive posts 6 on wiring substrate 4, and resin 7 is hardened.

Base material 5 is next removed (Step a) from wiring substrate 4 toexpose the opposite surface 3 b that is on the opposite side of surface3 a of wiring layer 3, as shown in FIG. 2D. In addition, solder resistlayer 9 is formed (Step b) on the opposite surface 3 b of wiring layer 3while leaving exposed portions 10 for exposing desired wiring of wiringlayer 3. The film thickness of solder resist layer 9 is a maximum of 20μm.

Resin 7, the rear surface of IC chip 1, and conductive posts 6 are nextsubjected to grinding to expose the end surfaces 8 of conductive posts6, as shown in FIG. 2E (Step c).

The order of Step a, Step b, Step c is not limited to the orderdescribed hereinabove and may be determined as appropriate according tothe manufacturing processes. The above-described procedure enables theformation of a thin planar semiconductor device that is shown in FIG. 1.

Explanation next regards the second embodiment example of thesemiconductor device of the present invention.

The semiconductor device of the second embodiment that is shown in FIG.3 is an assembled unit in which three of the semiconductor devices shownin FIG. 1 are stacked and electrically interconnected. Although thereare three stacked layers in FIG. 3, the present invention is not limitedto this number.

Referring now to FIG. 3, among vertically stacked semiconductor devices13, exposed portions 10 of wiring layer 3 that are not covered by solderresist layer 9 of one semiconductor device 13 are connected by solder 11to end surfaces 8 of conductive posts 6 that are provided on wiringlayer 3 of another semiconductor device 13. In addition, ball-shapedsolder 12 is affixed as electrode terminals to exposed portions 10 ofwiring layer 3 that are not covered by solder resist layer 9 oflowermost semiconductor device 13.

Ball-shaped solder may also be affixed as electrode terminals to endsurfaces 8 of conductive posts 6 of uppermost semiconductor device 13.

Stacking a plurality of layers of the semiconductor device shown in FIG.1 to form an assembly as shown in FIG. 3 enables an improvement in theintegration of semiconductor integrated circuits.

Explanation next regards the third embodiment of the semiconductordevice of the present invention.

The semiconductor device of the third embodiment that is shown in FIG. 4is a structure in which planar wiring layer 14 made up by electricalwiring is provided on surface 15 that is on the opposite side fromsolder resist layer 9 of the semiconductor device shown in FIG. 1, thisplanar wiring layer 14 being electrically connected to end surfaces 8 ofconductive posts 6.

In this construction, ball-shaped solder may be affixed as firstelectrode terminals to exposed portions 10 of the wiring of wiring layer3 as shown in FIG. 3, and moreover, ball-shaped solder may be affixed assecond electrode terminals to desired wiring of wiring layer 14. Ofcourse, a construction is also possible in which second electrodeterminals are not affixed to wiring layer 14.

While preferred embodiments of the present invention have been describedusing specific terms, such description is for illustrative purposesonly, and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the following claims.

1. A semiconductor device comprising: a wiring layer including a firstwiring, and said wiring layer having a first surface and a secondsurface opposing to said first surface, and said wiring layer having asolder resist layer provided on an exposed portion on said secondsurface; an IC chip having an electrode on a front surface and mountedon said first surface to be electrically connected to said first wiringvia said electrode by flip-chip bonding; a conductive post provided onsaid first surface to be electrically connected to said first wiring;insulating resin filling a space between said IC chip and saidconductive post to form an upper surface opposite to said first surfaceand to expose a rear surface of said IC chip and an end surface of saidconductive post; wherein: said rear surface and said end surface andsaid upper surface form a substantially flat and continuous surface. 2.The semiconductor device as claimed in claim 1, further comprising: asecond wiring on said second surface of said wiring layer.
 3. Thesemiconductor device as claimed in claim 2, further comprising: a thirdwiring formed on said upper surface to be electrically connected to saidend surface.
 4. The semiconductor device as claimed in claim 3, furthercomprising: a solder ball formed between said end surface and saidsecond wiring.
 5. The semiconductor device as claimed in claim 2,further comprising: a solder ball formed on said second wiring.
 6. Asemiconductor apparatus in which a plurality of semiconductor devices,according to claim 2, are stacked; wherein an end surface of one of saidplurality of semiconductor devices is electrically connected to a secondwiring of another of said plurality of semiconductor devices.
 7. Thesemiconductor device as claimed in claim 1, further comprising: a thirdwiring formed on said upper surface to be electrically connected to saidend surface.
 8. The semiconductor device as claimed in claim 1, furthercomprising: a solder ball formed on said end surface.